Diversity receiver system



April 25, 1950- B. TREVOR DIVERSITY RECEIVER SYSTEM Filed March 15, 1947 WVM/m? Trewz' Patented Apr. 25, 1950 illreyor, Riverhead, N. Y., assigner to iRadio `{lorporation n! America, a corprorationof Delaware Application 'Manch '15, 1947, Serial No. 734,980

( Cl. 'Z50-20) 2 Gleims. l

" "iin application I disclose improyed means efor selecting the strongest lof several versions of 'fthe same signal. Y

In my assigneeis communication :systems receivers in triple diversity are used for the :recep- 'tion of don-OEM -telegraphy signals and also for program material such as -voice, music, facsimile so orth. In these-systems, :the Awell known .arrangement of a common diode load resistor der @the 'three receivers is used mid the Vnegative ,po-

-cutput to the n'confirman load whereas :all tof the receivers getting weaker .signals fare blocked and 'do not simply output to ltheir diodes foi sume-lent magnitude to :overcome the Ibiases thereon to supaolltp'ut. In this manner, :selection o1 output trom the recel-yer getting the Vstrongest signal is made Ysind the selection is made at audio fre- 'duency The 4signal .selected at .audio frequency appears on `said common load eor a separate com- .mon load and is recorded if it is telegraphy, or

applied to :ami-io` frequency circuits if `voice or -music. v

It is desired to use said receivers in Acircuits where it :is necessary to make the signal Lselec- `tion at intermediate frequency/*rather than at audio frequency as is done in `said systems, For

example, it isdesired touse Acarrier exaltation the intermediate frequency stages .of adiyersi- `lied system and the best ,IFsgnal .carrier is to be:selectedr Y .Y Y .I .v

The primary obect .of my invention is to provide improved and simple means ci selecting the rstrongest loutput from a threeset .diversity re- --celver combination.

The gain control ,potential is'u'sediin common i automatic gain .control circuits in said above mentioned system. Thus, it may be said that the overall gains of 'the three receivers Aare maintained approximately the same; henceV the strongest signal at a particular recenter input will supply the strongest intermediate frequency output; In the case of lau exalted carrier receiver, it is n sometimes preferable to select the best 1F cutputbel'ore carrier exaltation anddetection. My selector unit accomplishes this selection-at intermediate .rrecrucney'and has the advantage of simplicity over'prior systems. *My invention is' 2 equally applicable .to ,many other uses Where the 'hat isignal of several :signals :is :to be selected for use.

.In the description igiven ,above land hereinatter, itis assumed receivers in triple .diversity are used. My invention equally :applicable to two receiver diversity systems. Y

1n .describing my invention ein detail, :reference `will be made to the attached ldrawings 'wherein 1the.singl'eflgure illustrates A:an embodiment :of my improved signal 'selector system. In the -drawings, there @are 'three .channels numbered In, 12 :and 3. It is assumed that carrier currents ,of :irelatiyelylow/requency such as, Afor example, of interrinediafte lirequency, modulated by the same signal and #derived :from Ldiversiiied sources, appear at channels 1|., 2 4and. i3. Moreover, it iis :assumed "that these signal :modulated :intermediate :frequency carriers are .of strengths or magnitudes `'uniiormly :related to received ysignals from which they are .fderivedsso that the strongest thereof may be said to The derived from the 1strongest signal received.

The intermediate frequency carrier on channel "the secondary winding of which 'is included -in a 'similarly tuned circuit 24; The circuit 24 is conjnected tothe control vgridlol a cathode follower stage tube 26 which supplies output for uses as desired over a lineftl; .As :will be described hereinaten the vstrongest intermediate frequency outfput is selected and supplied by circuits 20, '24 to amplifier 2.6 land put 'tojsucn use as desired.

VvThe `tubes it, IB and 1B" are in l.the'cir'cu-its whereinthe relative strengths ci the intermediate frequency carriers are in effect compared and used in yrectifiers to supply the control potentials ywhich determine whether or not tube .I t or W or 11"" will supply the useful output to tube 2'6. Tube It has its anode coupled to fa circuit 30 tuned to the intermediate frequency and including a windload resistor 3B. 'The resistor 36 is .shun-tedby' M XF iilter condensers :35' and 31 to remove voltage variations faster than those caused by variations in the average value of the IF currents. The diode 34 is so poled as to provide at the ungrounded or diode anode end of resistor 36 a negative potential, the magnitude of which depends on the strength of the signal fed to tube I6. Tubes I6' and I6" are each similarly connected by similarly tuned-circuits to similar rectiers and lters. The circuit couplings and elements in these connections have been designated by numerals corresponding to those used in the connections to the output electrode of tube I6 With primes added to those connected to tube I6 and double primes added t'o those connected to tube I6". The operation of the circuits then is such that across resistors 35, 36 and 36" ,inputs on.,.channels 2 and-3.` `The potential developed atthe point Awillbe more negative than the potentials at points B and C. For example, assume that a negative potential of approximately 12 volts is developed at the point A. This potentials are developed whichare negative and of magnitudes which increase as the strength of the signals applied tothe respective tubes it,

I5 and I6 increases These potentials are then compared as follows: The potential rappearing across the load resistor 36 is fed to one of the cathodes of a double diode 40 and one of the cathodes of a double diode 40". The potential developed across the resistor 36 is applied to one of the cathodes of the double diode 4I) and one of' the cathodes of the double diode 40". Thel potential developed across the load resistor 3B is applied to one of the cathodes of the double diode 40 and to one of the cathodes of the double diode 40. The diodes 4|l, 40' and 40 may be considered valves since the same will not operate unless the cathodesY thereof are negative with respect to the anodes. The anodes of the diodes 4I? are` tied together and connected to the control grids of tubes I4 and I6 by bias resistor 4I.- These anodes are also connected by resistor 42 and lead 45 to a source of potential which is negative with respect to ground and/or the cathodes of all of the tubes I4, I6, I4', I6', I4" and I5". Both anodes of tube 49' and tube 49 are similarly tied together and connected to the control gridsofv tubes I4', I5 and I4 and I6 respectively. lThe anodes of these double diodes are also similarlyl connected by resistors-42 and 42 to said negative potential source.

A source of supply potentials including voltage regulating tubes is shown at 5D and the showing is self explanatory. Voltage regulator'tubes are included since constant D. C. potentials are desirable in the signal selector circuits. Milliammeters M may be used throughout the circuit as desired for adjustment and tuning purposes.

The operation of the system is vas follows:

The voltages at the points A, Band C-- are negative relative Vto ground by amounts which are 'a measure of the magnitude of the intermediate frequency -at inputsv IIL-'Ill'gand III". The bias developed at point A, when negative enough to overcome the xed negative bias fed by resistors 42 and 42 to the anodes ofthese diodes, is fed by one side ofA double diodev 40" and by one side of doubleV diode 40 to the control grids of tubes I6", I4 and I6 and I4"respec:

tively. The bias developedrat point B -when negative enough to overcome theixed negative bias fed by resistors-42 and 42 to the anodes of these diodes, is fed by one side of double diodes 40" and 40 to the control grids of tubes I6" I4", and I6, I4 respectively. The bias developed lat point C when negative enough to overcome the fixed negative bias fed by resistor 42-'- and42 Ato `the 'anodes `of'thesediodes is fed by one sideof potential is applied to the cathodes of one of the diodes in tube 40' and one of the diodes in tube 40". The negative potential on the anodes thereof applied by resistors 42', 42 might be, for eX- ample, minus 3 volts. Then, the said diodes would have their anodes more positive than their cathodes and would be conductive. The anodes thereof would become more negative by an amount equal to the` fixed-potential plus a portion ofthe l2 volts developed at A. This potential is made to be sufficient to bias tubes I6 I4, I6' and I4' to cutoff so that they do not supply intermediate frequency energy to their diodes to develop high negative potentials at the points'B and C. Hence, points B and C do notfeed negative potential through the double diodes of tube 40 to cut oil the tubes I6 and I4. 'Ihe action of diode 40 then is such as to feed only thexed negative potential through resistor 42, and 4I to the control grids of tubes I6 and I4. These tubes then operate in a normal class A manner to supply output to tube 26 for use as desired -and to supply intermediate frequency energy to the rectier 34 to maintain the remaining channels blocked as long as the signal in channel 'I is the strongest. In this nanner, channel'I supplies'the'used output as long as its signal is strongest. If the input to channel I decreases and the input to channel 2, for example, increases and becomes the strongest signal, then a sudden switching action takes place because the potential developed at B becomes more negative, say approximately l2 volts, to apply negative bias through double diodes 40 to the control grids of tubes I6 and I4 andjalso through double diode 40" to the control grids of ,tubes I6" and I4".

Then these latter tubes are cut o'and output'is supplied as described hereinbefore from tube I 4 connected at its input to channel 2.v The Ytube I6 is then also operating classv A to maintain the negative potential at B as long as the signal on channel 2 is strongest. y, r Y vThe circuit then is a -three-way trigge'r switcher `operating in such "a, manner lthat only one receiver at a 'time can contribute to theoutput except during the briefswitch-oveif periods which occur when oneinput isjdroppng andthe other increasing in amplitude.:v 4 y The diodes 40, 40' and 40" iare provided ftp give one-way pathsgtov feed negative bias'hfrcmv poil-1135 A, .B and C to the control. grdsjrofvthe .amplifier tubes. This'providesproper isolation between the three channels and allows the .negativey threevolt --to gang 4the potentiometersllfI2-and |21', yin double diodes 40 and 40 to-thecontrol grids ofwqsorder -to-faci1itate Vthe lproper signal levelinput to derive the switching action described hereinbefore.

The signals in channels I, 2 and 3 may be derived from a diversity system such as shown by block diagram in the figure. The three antennas X, X and X supply input to three receivers R, R and R each comprising radio frequency ampliers, a frequency converter, and intermediate frequency ampliers. These receivers supply output to intermediate frequency stages IF, IF and IF wherein further frequency conversion may take place when desired. Each of the intermediate frequency stages may include a rectifier which supplies a. common load CL. The potential developed across CL is used for automatic gain control purposes, and then the signal strength on channels I, 2 and 3 will be a measure of the strength of the signals received on the respective antennas X, X and X".

What is claimed is:

1. In means for sensing the strongest of at least two carrier currents in at least two channels, a rectier circuit for each current and channel, a load impedance in each rectier circuit, means for feeding each of the currents to its respective rectifier circuit, an impedance for each current and in each channel at which impedances potentials are to be set up which are measures of the relative magnitudes of the said currents, a pair of one-way valves for each of said last named impedances, said valves each having an input electrode and an output electrode, the output electrodes of each pair being tied together and coupled to their corresponding measuring impedance, and means for feeding the potential developed in each of said rectier circuit load impedances to the input electrodes of the valves connected to all of said impedances except to those two valves connected to the measuring impedance corresponding to the current and channel producing the developed potential.

2. In means for sensing the strongest of at least two carrier currents in at least two channels, a rectifier circuit in each channel, a load impedance in each rectifier circuit, means for feeding each of the currents to its respective rectifier circuit, an impedance for each current and in each channel at which impedances potentials are to be set up which are measures of the relative magnitudes of the said currents, a pair of one-way valves connected to each of said measuring impedances, and means for feeding the rectified potential in each or" said rectifier circuit load impedances to all of said measuring impedances except that one corresponding to the current and channel producing the said rectied potential, said last-named means including one of said oneway valves in each of the connections between the rectifier load impedances and the said measuring impedances.

BERTRAM TREVOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,792,312 Labus Feb. 10, 1931 2,171,657 Klotz Sept. 5, 1939 2,200,049 Van Loon May 7, 1940 2,249,425 Hansell July 15, 1941 2,414,111 Lyons Jan. 14, 1947 

